Process of hardening and simultaneously increasing the sensitivity of photographic silver halide emulsions



Fatented July 1, 1941 UNITED STATES PATENT FF1E PROCESS OF HARDENING AND SHVI'ULTA- NEOUSLY INCREASING THE SENSITIVITY 0F PHOTOGRAPHIC SILVER HALIDE EMULSIONS No Drawing. Application February 28, 1940, Se-

rial No. 321,208. 1939 4 Claims.

This invention relates to hardening and simultaneously increasing the sensitivity of photographic silver halide emulsions. Aldehydes and ketones, for instance formaldehydes, glyoxal, exyketones, are generally used for the hardening of photographic emulsions. All of these hardening agents however show the disadvantage to continue the hardening process later on during storage, which decreases the sensitivity and gradation of the emulsion.

It is an object of this invention to provide a process of hardening photographic silver halide emulsions.

A further object resides in the provision of a hardening agent, which increases the sensitivity of the silver halide emulsion.

A still further object is the provision of an emulsion containing said hardening agent.

Still further objects will appear from the detailed specification following hereinafter.

It has been proposed to harden photographic silver halide emulsions with the aid of basicly substituted aldehydes and to simultaneously increase their sensitivity. This compensates the decrease suffered in sensitivity as well as in gradation, which usually occurs during storing. To the aldehydes suitable according to this invention belong aliphatic aldehydes, containing a free or a substituted NI-I2 group. In the latter case the amino groups may be substituted by alkyl radicals. But also such substituted aldehydes may be applied, which contain a ring substituent with a nitrogen atom in the nucleus. The following compounds serve as an example: aminoacetic aldehyde, aminodiacetic aldehyde, diethyl aminoacetic aldehyde, piperidinoacetic aldehyde, ,B-diethylamino propionic aldehyde and functional derivatives like aminoacetic aldehyde bisulfite and the respective oxime. The hardening agent may be added to the finished emulsion before casting. It may be applied in every phase during the manufacturing process of the emulsion, it may serve as preliminary bath before developing or be added to the developer itself. Needless to say these hardening agents like all others hitherto known may be applied to harden the emulsion layers after development, and to harden also other substances and structures influenced by aldehydes. In this case however the characteristics of the hardening agents, to increase simultaneously the sensitivity of the emulsion, have no practical efiect.

ExampZeI 0.5 gram piperldino acetic aldehyde chlorine assignors to General In Germany February 9,

hydrate is added to 1 kg. X-ray emulsion and cast in the usual way. The melting point is driven to 35 C. for the fresh emulsion, whereas the melting point for the corresponding test emulsion without hardening agent lies at 32 C. The increase in sensitivity accomplished by adding the hardening agent is very considerable. During storage the melting point increases to 46 C., but the sensitivity remains clearly above the one of the not-hardened starting material.

Example II wherein R1 and R2 are selected from the class consisting of H and alkyl, R3 and R4 are alkylene and n stands for the number 1 and 2:.

2. A process of hardening photographic emulsions which comprises adding to a photographic silver halide gelatin emulsion amino-acetaldehyde.

3. A process of hardening photographic emulsions which comprises adding to a photographic silver halide gelatin emulsion diethylamino-acetic aldehyde.

4. A process of hardening photographic emulsions which comprises adding to a photographic silver halide gelatin emulsion piperidino acetic aldehyde.

JOHANN'ES BRUNKEN. HANS FRICKE. GUSTAV WILMANNS. 

